Recent years, in response to the needs for electronic devices such as miniaturization, speeding up, integration, and multifunctionality, the manufacture of devices containing functional materials such as electronic ceramics, which express predetermined functions by being applied with electric fields or magnetic fields and include a dielectric material, piezoelectric material, magnetic material, pyroelectric material and semiconductor material, by using various film formation technologies has been actively studied.
For example, in order to enable high-definition and high-quality printing in an inkjet printer, it is necessary to miniaturize and highly integrate ink nozzles of inkjet heads. Accordingly, it is also necessary to similarly miniaturize and highly integrate piezoelectric actuators for driving the respective ink nozzles. In such a case, a film formation technology, that enables formation of a thinner layer than a bulk material and formation of fine patterns, is desired, and film formation technologies such as a sputteringmethod, a sol-gel method, and an aerosol deposition method have been studied.
However, there has been a problem that a film of function material (also simply referred to as “functional film”) formed by film formation does not sufficiently exert its function in a condition after the film formation, and the film is inferior to a bulk material in performance.
In order to sufficiently express the function of a functional film, heat treatment at relatively high temperature (e.g., about 500° C. to 1000° C.) is required after film formation. Since a substrate that is used at the time of film formation (film formation substrate) is simultaneously heat-treated, high heat tolerance is required for the material of film formation substrate. On the other hand, in the case where a fabricated function film is utilized, there is demand for using various kinds of substrates according to instruments such as a flexibly substrate made of resin, for example. Accordingly, a method has been studied by which a functional film formed on a film formation substrate can be peeled from the film formation substrate without hindering its function.
As a related technology, Japanese Patent Application Publication JP-A-54-94905 discloses a multilayered structure for thin film transfer having a heat-resistant substrate, a release layer principally containing carbon and/or carbon compound, and a functional thin film as main component elements (pages 1 and 3). Further, JP-A-54-94905 discloses that the functional thin film can be peeled from the heat-resistant substrate and transferred to another substrate because the release layer can be removed by oxidization (combustion).
Japanese Patent Application Publication JP-A-10-125929 discloses a peeling method by which any material to be peeled can be easily peeled regardless of its properties or conditions, and especially, the peeled material can be transferred to various transfer materials. The peeling method is to peel a material to be peeled existing on a substrate via a separation layer having a multilayered structure of plural layers from the substrate, and includes the step of applying irradiating light to the separation layer to cause peeling within the layer of the separation layer and/or at an interface thereof so as to detach the material to be peeled from the substrate (pages 1-2).
Japanese Patent Application Publication JP-P2002-305334A discloses a method of transferring a functional thin film in order to obtain a less defective functional thin film by easy and perfect peeling at the interface between a functional thin film structure and a separation layer. That is, the method is to transfer a functional thin film formed on a first substrate onto a second substrate, and includes the steps of forming a separation layer containing a metal nitride layer on the first substrate, subsequently forming a functional thin film structure containing oxygen directly on the separation layer, providing the second substrate on the functional thin film structure, forming an oxide layer by oxidizing the separation layer at the functional thin film structure side by heating, and peeling at the interface between the oxide layer and the functional thin film structure so as to transfer the functional film structure formed on the first substrate onto the second substrate (page 1).
However, according to JP-A-54-94905, since the release layer is removed by oxidation reaction, the atmosphere in the heat treatment process is limited to an oxygen atmosphere. Further, since carbon or carbon compound is used as the release layer, there is the upper limit to heating temperature. For example, in an embodiment disclosed in JP-A-54-94905, the treatment temperature in the transfer process is 630° C. at the highest. Therefore, the present invention disclosed in JP-A-54-94905 cannot be applied to a manufacture of electronic ceramics that requires heat treatment at relatively high temperature (e.g., 900° C. or more).
Further, according to JP-A-10-125929, peeling is caused within the separation layer by applying a laser beam to a light absorption layer contained in the separation layer to allow the light absorption layer to ablate. Since the irradiating light is applied to the separation layer via the substrate, the substrate requires translucency. Accordingly, the method is not preferable because the substrate material is limited.
Furthermore, according to JP-P2002-305334A, since the complex multilayer structure containing the nitride layer and oxide layer is formed, the process is complicated and the cost of manufacturing may rise. Further, according to JP-P2002-305334A, the metal nitride layer contained in the separation layer changes into oxide by heat treatment, and thereby, stress is caused at the interface between them and the adhesion is reduced. Since they are mechanically torn off by the reduction in adhesion, it is conceivable that there is a problem in peeling property.